An image sensor is a semiconductor device used to convert optical images detected by the image sensor to electric signals. Image sensors may be classified as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS).
A CCD image sensor is provided with metal oxide silicon (MOS) capacitors that are spatially positioned within close proximity to each other and charge carriers are stored in and transferred to the capacitors.
A CMOS image sensor may be provided with a plurality of MOS transistors corresponding to pixels of a semiconductor device having a control circuit and a signal processing circuit as peripheral circuits. The control circuit and the signal processing unit may be integrated together to employ a switching method that detects output through the MOS transistors. In a CMOS image sensor, as light intensity of the photodiode increases, photosensitivity of the image sensor may be further enhanced.
The CCD image sensor is considered superior to the CMOS image sensor in terms of photosensitivity and noise reduction but has difficulty in achieving highly integrated density and low power consumption. Moreover, the CMOS image sensor is simpler to manufacture and can be more suitable for achieving highly integrated density and low power consumption. Accordingly, aspects of semiconductor fabricating technology have focused on developing a CMOS image sensor due to its qualities in addition to enhanced fabricating technology.
In order to raise photosensitivity in image sensors such as CMOS image sensors, a fill factor, which indicates a ratio of a photodiode size to a total size of an image sensor, may be increased or a microlens is provided in order to condense light into the photodiode by changing a path of light incident on an area except the photodiode.
As illustrated in example FIG. 1, an image sensor may include device isolation layer 12 formed on and/or over semiconductor substrate 10. Device isolation layer 12 may define an active area of semiconductor substrate 10.
A plurality of photodiodes 14 may be provided on and/or over semiconductor substrate 10. Photodiodes 14 may be formed in an active area of semiconductor substrate 10 in order to generate charges according to the intensity of incident light.
Insulating interlayer 16 and insulating layer 18 may be formed on and/or over semiconductor substrate 10 including device isolation layer 12 and photodiodes 14. Insulating interlayer 16 can be formed to cover photodiodes 14 while insulating layer 18 can be formed on and/or over insulating interlayer 16. Passivation layer 20 may be formed on and/or over semiconductor substrate 10 including insulating layer 18.
A plurality of color filters 22 may be formed on and/or over semiconductor substrate 10. Color filters 22 may include color filters composed of red R, green G and blue B. Planarization layer 24 may be formed on and/or over semiconductor substrate 10 including passivation layer 20 and color filters 22. Planarization layer 24 may serve to planarize the surface of color filter 22.
A plurality of microlens 26 may then be provided on and/or over semiconductor substrate 10 including color filter 22 and planarization layer 24. Each microlens 26 can be formed on and/or over planarization layer 24 to oppose a corresponding color filter 22 and condenses light into the corresponding photodiode 14. Each microlens 26 can also be fabricated to have a convex figure with a predetermined curvature in order to externally condense incident light to color filters 22. Color filters 22 may then transmit specific wavelengths of red R, green G and blue B of the projected light to implement colors. Photodiodes 14 may then convert energy of the transmitted light into electric energy.
A packaging process may be conducted on the image sensor. As illustrated in example FIG. 2, external lens 30 can then be attached over the image sensor. The incident light from external lens 30 normally forms an image on a center of the image sensor. Yet, since intensity of light incident on photodiodes 14 becomes reduced toward edges A and B of the image sensor, it is difficult to form a normal image. Accordingly, if intensity of light incident on a unit pixel varies according to the center or edge of the image sensor, the number of electrons generated from photodiode 14 may also vary.
Although an original image has the same color, an image color at the center of the image sensor may be displayed differently from that at the edge of the image sensor. Moreover, crosstalk, i.e., the optical interference between pixels on the edge of the image sensor, may occur to significantly degrade reliability of the image sensor.